Atherosclerosis is a progressive disease of the vascular system whereby atheroma is deposited on the inner walls of blood vessels. Over time atheromatous deposits can become large enough to reduce or occlude blood flow through the vessels, leading to symptoms of low blood flow such as pain in the legs (on walking or at rest), skin ulcer, angina (at rest or exertional), and other symptoms. To treat this disease and improve or resolve these symptoms it is desirable to restore or improve blood flow through the vessel.
Various means are used to restore or improve blood flow through atheromatous vessels. The atheroma deposits can be displaced by diametrically expanding the vessel by inflating balloons, expanding stents, and other methods. However these methods undesirably tear and stretch the vessel, causing scar formation in a high percentage of patients. Such scar tissue (restenotic material), once formed, blocks flow in the vessel and often needs to be removed. The deposits can be pulverized using lasers and other methods. However pulverization alone of atheromatous material allows microemboli to flow downstream and lodge in distal vascular beds, further compromising blood flow to the tissue affected by the disease. Atherectomy catheters can be used to remove atheromatous deposits from the blood vessel and can present an ideal solution when the atheromatous debris removed from the vessel is captured and removed from the body.
One problem that occurs when removing material from a blood vessel is that the material may be either soft or hard. Typically, restenotic scar is soft yet tough while atheroma varies in texture from soft with little structure, to soft yet fibrotic, to densely fibrotic (hard). Any or all of these restenotic or atheromatous tissues may be calcified and the calcified tissues can be extremely hard. The hardness and toughness characteristics of the material needing to be cut from the vessel may vary along the length of the vessel, around the circumference of the vessel, or both. Further, the portion of the vessel to be treated can be quite extensive. For example, the portion of the vessel to be treated can extend over a vessel length of 200 mm or longer. As such, the cutting element of an atherectomy catheter should be able to cut both hard tissue and soft tissue.